A capacitive humidity sensor, disclosed in JP-U-5-23124, has a humidity sensitive layer interposed between a pair of electrodes. Relative permittivity of the humidity sensitive layer is changed in response to humidity.
In this sensor, the electrodes are arranged opposite to each other on a surface of an insulating substrate, and the humidity sensitive layer (a dielectric material) is disposed on the electrodes. Further, a circuit section such as a signal processing circuit for a capacitance change between the electrodes is disposed in a substrate separated from the insulating substrate. Therefore, the electrodes are required to be electrically connected to the circuit section using bonding wires or lead wires or the like. Therefore, it is difficult to reduce the whole size of the sensor including the circuit section.
In a capacitive humidity sensor disclosed in U.S. Pat. No. 6,580,600 (corresponding to JP-A-2002-243690), a pair of electrodes and a humidity sensitive layer are integrated with a circuit section on a semiconductor substrate. The electrodes are electrically connected to the circuit section through wiring formed on the semiconductor substrate. Therefore, the whole size of the sensor can be reduced.
In the sensor using a semiconductor substrate, however, semiconductor process technology is essential to form the electrodes, the humidity sensitive layer and the circuit section. Therefore, complex process and expensive equipment are required to manufacture the sensor in addition to high cost of a semiconductor substrate. Accordingly, the manufacturing cost of the sensor increases.